Hi,
> It appears to me that the origin on the MNI template (any of them, 152, 305,
> Colin) is not on the Anterior Commissure; and it seems that others agree:
> http://www.mrc-cbu.cam.ac.uk/Imaging/Common/mnispace.shtml
> "...the coordinates are reported in terms of the system that Talairach
> developed, with coordinate 0,0,0 being at the anterior commissure (AC), and
> with the anterior / posterior commissural line (AC/PC line) defining the the
> plane where z = 0. (In fact the AC is not exactly at 0,0,0 in the MNI brain,
> but about 4mm below...)"
>
> My first question is: Why is the origin off, or how was the origin determined?
The algorithm the MNI used was rather complex, and didn't quite get the
AC at the AC. It's not as far off as it looks though, as Talairach
specified the inferior border of the AC as the landmark, as I remember.
I don't think this is the major problem though, as the T atlas itself is
so approximate that a mm or two won't make much difference. The real
problems are in the temporal lobes, where there are 10mm differences -
and this can really effect meta-analyses of - say - amygdala activation.
Best,
Matthew
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